Pulse-shaping experiments in a 100 Am thick CdS etalon have been performed with a pulsed frequency-doubled Nd-YAG laser. The incident laser pulse produces changes in the refractive index, and the CdS etalon is tuned over a few resonances. From these experiments a refractive index change in CdS of An = 0.0035 can be estimated. We also report pulse-shortening experiments with the CdS etalon. Finally, we have investigated the self-refraction of Gaussian laser beams in the CdS sample. We observe self-defocusings, which indicate that the dominant mechanism for the nonlinear refraction is not of thermal origin.